Neurological Recruitment Underlying the Positivity Effect in Memory
We begin this section by examining what we know about the emotional memory network and the degree to which corresponding brain structures decline or are preserved with increasing age. Interestingly, the regions implicated in emotional processing such as the ventromedial prefrontal cortex (VMPFC) undergo relatively modest structural changes with aging, and the amygdala is relatively structurally preserved with aging (Raz,
1996) . In contrast, other regions of the prefrontal cortex (PFC) undergo a more rapid and earlier pace of decline, such as the dorsolateral regions of the PFC (Raz, 1996). Even more importantly, it is necessary to examine the function (i. e., activation) of emotion processing regions of the brain across the adult life span.
LaBar and Cabeza (2006) describe a core emotional memory network that consists of the amygdala, hippocampus, and lateral orbitofron – tal cortex. Activation in these areas relate to the successful encoding of emotional information in general. Again, these regions are well preserved in emotional memory as one grows older. Indeed, for both younger and older adults, activation of the amygdala and lateral orbitofrontal cortex corresponds to memory performance for both positive and negative items (Kensinger & Schacter, 2008). There are also areas in the brain beyond this
emotional core that are more valence-dependent. For example, for both younger and older adults, the occipito-temporal regions (more specifically the fusiform gyrus) are more likely to be recruited during successful encoding of negative information, whereas anterior prefrontal regions are activated during successful encoding of positive information (Mickley & Kensinger, 2008).
Neuroimaging studies reveal differential age – related activation of neural substrates that might help us understand the neurological mechanisms underlying the positivity effect. For example, older adults show activation of the medial prefrontal cortex and regions of the cingulate gyrus when responding to positive stimuli whereas younger adults do not (Kensinger & Schacter, 2008). Similarly, compared to the young, older adults show greater amygdala activation for positive pictures than for negative ones (Mather et al., 2004). Such findings indicate that it may not be overall decline in functioning of the amygdala that causes age-related responding to emotional stimuli, but rather a shift in the type of emotional stimuli to which the amygdala is most responsive (Leclerc & Kensinger, 2008).
Finally, another intriguing possibility raised in the literature is that the positivity effect may arise from changes in controlled emotional processing or emotion regulation (Leclerc & Kensinger, 2008; Mather & Knight, 2005). It is proposed that the positivity effect should be seen only when an individual has a high degree of cognitive control resources. If these resources are limited, this reduces the ability to regulate responses to emotional information. Accordingly, older adults who are low in resources show no positivity effect (Mather & Knight, 2005).
Research conducted in different domains of emotional processing also has demonstrated age – related differences in brain activation. For example, fMRI studies have found age differences in brain activation when viewing faces with negative emotional expressions (e. g., Anderson, Christoff, Panitz, De Rosa, & Gabrieli, 2003). Younger adults show increased activity in the amygdala when
viewing negative emotional expressions, whereas activity in the amygdala is reduced in older adults when viewing these faces. Interestingly overrecruitment of areas such as the anterior cingulate gyrus is increased in older adults when viewing these faces (Gunning-Dixon et al., 2003). This is quite reminiscent of the compensation models discussed in the context of cognitive aging and neuroscience perspectives.
Overall, findings in this line of research have revealed that the core emotional memory network is preserved with aging. Age-related differences are most evident in the successful encoding of positive information as opposed to processes contributing to the memory for negative information. Thus, the structural preservation with increasing age of various regions in the cortex may subserve the preservation of emotional processing.
1. How does emotional processing differ from cognitive processing in older adulthood?
2. How does the neural circuitry operate when younger and older adults process emotional information?
3. How do age-related changes in brain structure account for the positivity effect found in older adults?
Neuroscience as a Basis for Adult Development and Aging 59